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[[File:1200px-Cow_female_black_white.jpg|thumbnail|275px|Holstein-Friesian Daily Cow]]
We take for granted today that dairy consumption is something that is typical or even natural to human diet. However, that is not the case, as it contains lactose, a complex carbohydrate that is not digestible in most adult mammals.<ref> For lactose ingestion in mammals, see: Sahi, T. 1994. “Hypolactasia and Lactase Persistence Historical Review and the Terminology.” ''Scandinavian Journal of Gastroenterology'' 29 (s202): 1–6. dos:10.3109/00365529409091739. </ref> In other words, the vast majority of human beings, at one point, were physically unable to consume dairy products after their childhood; in fact, we see today a large percentage of people still unable to consume milk or dairy products in adulthood. This leads to the question on how did human societies become or evolve to the point where dairy consumption became prevalent?
==Evolution and Agriculture==
Natural selection, the process first uncovered by Charles Darwin, tells us that specific traits, over time, could become selected for, leading to a transformed species as given traits become advantageous for reproduction.<ref>For information on the process of natural selection, see: Endler, John A. 1986. ''Natural Selection in the Wild''. Monographs in Population Biology 21. Princeton, N.J: Princeton University Press.</ref> Dairy consumption, in fact, is an example of how relatively recent natural selection pressures have transformed our human DNA. Over 11,000 years ago, that is before the invention of agriculture, almost all societies depended on hunting and gathering. Their diets were much more diverse than ours and consumed a large variety of meats, fruits, and vegetables.<ref> For information on the human diet in pre-agricultural societies, see: Hockett, Bryan, and Jonathan Haws. 2003. “Nutritional Ecology and Diachronic Trends in Paleolithic Diet and Health.” ''Evolutionary Anthropology: Issues, News, and Reviews'' 12 (5): 211–16. dos:10.1002/evan.10116. </ref> However, dairy was not a caloric resource they would have typically encountered during adulthood.
During the rise of agriculture in the Near East at about 11,000 years ago, we see that sheep, goats, and cows were among the earliest animals domesticated. Other early domesticates include dogs and pigs. As all mammals produce milk, this led to early agricultural villages having now far greater dairy resources naturally available. Initially, very likely dairy would not have been easily consumed by adults and perhaps even avoided; however, genetic mutations naturally show a very small percentage of the human population would have had alleles or groups of genes that allow for the consumption of dairy later in life (i.e., they are lactose persistent).<ref> For genetic information about lactose persistence in pre-agriculture humans, see: Knapp, Michael, Carles Lalueza-Fox, and Michael Hofreiter. 2015. “Re-Inventing Ancient Human DNA.” ''Investigative Genetics 6'' (1). dos:10.1186/s13323-015-0020-4.</ref>
[[File:World_map_of_lactose_intolerance.png|thumbnail|350px|World Map of Lactose Intolerence]]
This is made possible by the production of the lactase enzyme need to breakdown lactose into digestible carbohydrates. With greater availability of milk in early settled societies, the advantages of having a high caloric product that has calcium and fats that are beneficial became a greater selective pressure for human populations. The genes that then produce the lactase enzyme became selected for or gave advantages to given human populations that then allowed the consumption of lactose found in diary. The fact that milk was utilized very early in the Near East has meant that populations there do show a relatively high ratio of lactose persistence in adulthood (Figure 1).
==Coevolution of Dairy==
The story of how dairy developed as a product of consumption is, however, more complex. Once agriculture was invented, it did begin to spread to Europe, initially in southeast Europe before spreading to northern and western Europe.<ref>For tracing the spread of agriculture, see: Pinhasi, Ron, Joaquim Fort, and Albert J Ammerman. 2005. “Tracing the Origin and Spread of Agriculture in Europe.” Edited by Chris Tyler-Smith. ''PLoS Biology'' 3 (12): e410. dos:10.1371/journal.pbio.0030410.</ref> Looking at a modern map of populations that are lactose persistent (Figure 1), we see pockets where particular populations have a much greater portion of the population able to consume dairy. This indicates that the spread of dairy consumption was not even and that different populations have adapted differently to dairy consumption. In Europe, we see eastern Europe, around Poland and the Czech Republic, there is a greater percentage of people who are lactose persistent. A closer look at the haplotypes, or genetic groups, that include the genes for dairy consumption indicate that not all human populations that have evolved to consume dairy show the same genes involved in the consumption of lactase.<ref>For further on the genetic makeup of Europeans in relation to the consumption of diary, see: Leonardi, Michela, Pascale Gerbault, Mark G. Thomas, and Joachim Burger. 2012. “The Evolution of Lactase Persistence in Europe. A Synthesis of Archaeological and Genetic Evidence.” International Dairy Journal 22 (2): 88–97. doi:10.1016/j.idairyj.2011.10.010.</ref>
In other words, there are multiple evolutionary tracts that have led to the consumption of milk around the world. This happens due to the process of coevolution, when different environmental factors lead to evolutionary changes that result in similar adaptations but involve different gene groups. In fact, there are different divergences known to us in relation to dairy consumption; dairy we know has become one of the strongest factors in early human societies fitness and likely helped societies to survive particularly in times of famine.<ref>For the coevolutionary paths of dairy, see: Gibson, Greg. 2007. “Human Evolution: Thrifty Genes and the Dairy Queen.” Current Biology 17 (8): R295–96. doi:10.1016/j.cub.2007.02.011. </ref> The different evolutionary changes across different societies have allowed different populations to consume dairy as adults. The invention of agriculture in the Near East is, in essence, only part of the story.
==What Archaeology Tells Us==
[[File:894px-GBM_-_Linearbandkeramik_7.jpg|thumbnail|300px|Linear Pottery from Bavaria]]
To better understand how milk became consumed by different human societies we need help from archaeology. This is very clear in Europe, where many early Neolithic sites have been dated using radiocarbon dating techniques. Looking at the regions where early agriculture and milk consumption occurred, including ceramics that show evidence of milk being processed within them, and cow bones have been found, we can trace regions in Europe where the population after the arrival of agriculture from the Near East began to be more dependent on cattle.<ref>For a discussion on archaeological remains related to dairy, see: Oliver E. Craig, John Chapman, Carl Heron, Laura H. Willis, László Bartosiewicz, Gillian Taylor, Alasdair Whittle and Matthew Collins (2005). Did the first farmers of central and eastern Europe produce dairy foods? Antiquity 79: 882-894.</ref> We know in the ancient Near East that sheep and goat were more utilized. However, in central and eastern Europe, cattle became preferred and this led to more consumption of cow milk.
What the evolution of milk consumption shows is that recent evolutionary pressures are still affecting how modern humans evolve. Dairy consumption in adulthood has only recently evolved, given its selective pressures for early agricultural societies. It is a complex history, with multiple evolutionary paths, but indicates that it became important for many societies. The consumption of milk has been one of the most important recent evolutionary changes in the human genome, as it allowed dairy to be consumed at a large scale for the first time. Given dairy’s importance to early farmers, this change led to the exploitation of new food resources, allowing human populations and settlement to expand to new areas. Over time, this had a transformative effect for human populations and their economic societies.
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